How to choose an energy efficient air conditioner

Avleen M.
Avleen M.Published on 25 Oct 2021

Energy efficient air conditioners give you cut-price energy bills, and minimise your carbon footprint by reducing those pesky emissions. They also cool air faster, maximising comfort. However, they are also pricier to buy. Ultimately it’s your decision to opt for a cheap air conditioner, or wait for the long-term energy savings to trickle in. Continue Reading...

The new Zoned Energy Rating Label

Also known as the ZERL, this is a new standardised way to measure energy efficiency on air conditioners and heaters.

Air conditioners sold in Australia from April 2020 and onwards will have the new ZERL rating on them. It was designed to make it easier to know how energy efficient a cooling or heating appliance is, specific to where you live in Australia.

Here are some of the things to look out for on the new energy rating.

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Climate-specific star ratings

The new rating system awards stars based on where you live in Australia. All major cities are divided into 3 distinct climate zones - Hot, Average or Cold. For example, Brisbane is considered Hot, Sydney has Average temperatures, and Melbourne is considered Cold. Energy efficiency is rated according to your zone.

Stars out of 10

Under this rating, energy efficiency is measured as a star rating out of 10 (compared to the old system of rating energy efficiency out of 6 stars). Stars for cooling are coloured in blue, and stars awarded for heating performance are in red.

Yearly energy use estimate

This specifies an estimated number of kWh per year for heating and cooling, based on your temperature zone. A lower kWh per year means less energy consumption, and a cheaper electricity bill.

If you know the hourly rate of your electricity tariff - which averages $0.29 nationally - you can multiply the number of kWh per year on the ZERL by your rate, to get an approximate yearly running cost.

The method the government uses to calculate this annual electricity usage figure on an AC label is based on average consumer use patterns. Your figure will varies based depending on how frequently you run the AC in your household.

Portable air conditioners are now rated

Under the old energy rating label, portable air conditioners and ducted AC systems were not required to have an energy efficiency rating. It’s now mandatory for portable ACs to have a ZERL energy efficiency rating.

Ducted systems and evaporative coolers are still not required to carry an energy label.

The old energy rating label

If the air conditioner you’re looking at buying was offered for sale before April 2020, it will have the old energy rating label on it.

This label shows a star rating out of 6 possible stars as a standard. Air conditioners can also be awarded a ‘super efficiency rating,’ with up to 4 more stars, for a rating out of 10.


A note on comparing air conditioners

When comparing the energy efficiency of two air conditioners, first make sure they use the same rating system.

Unfortunately, the energy rating of an AC using the old star system can't be pitted against one that uses the new energy label.

How to compare air conditioners that use different energy ratings

However, there are other ways to compare energy efficiency. It may take a bit of digging to find a unit's full specs. Sometimes this information is available on retailer websites but not the manufacturers’ website, or vice versa.

Here are some things to compare:

  • Energy Efficiency Ratio (EER): This refers to Cooling output capacity divided by Cooling input. A higher EER is more energy efficient.
  • Cooling input: A lower input is better, and means the AC will require less power to cool the same-sized room as a competitor model.
  • Cost of yearly energy consumption: Calculated as estimated kWh used per year multiplied by your hourly electricity tariff.

Here is a practical example comparing one of the best-rated split system reverse cycle air conditioners on, to a cheaper, less energy efficient model of the same kind.

In terms of the most energy efficient split system air conditioner here, the winner is the Mitsubishi model.


Mitsubishi Heavy Industries Avanti Series

Braemar BSHV25D1S

Cooling power

2.5kW (small room)

2.6kW (small room)

Cooling input

0.51 kW

0.68 kW

Heating input

0.65 kW

0.73 kW

Energy Efficiency Ratio (EER)




Around $800

Around $670

How do I calculate the cost of running an air conditioner?

Using the example of the two air conditioners above, these costs are calculated on the basis of running the appliances for 3 hours every day in summer, and 3 hours every day in winter.

Mitsubishi Heavy Industries Avanti Series

Cooling cost per year

  • 0.51kW input per hour x 270 hours (3 hours x 90 days) = 137.7 kWh per year
  • 137.7kWh x $0.29 hourly electricity rate = $39.93

Heating cost per year

  • 0.65kW input ph x 270 hours = 175.5 kWh per year
  • 175.5 kWh x $0.29 per hour = $50.90

Combined costs for heating and cooling = $90.80

Braemar BSHV25D1S

Cooling cost per year

  • 0.68kW input per hour x 270 hours (3 hours x 90 days) = 183.6 kWh per year
  • 183.6kWh x $0.29 hourly electricity rate = $53.24 for cooling

Heating cost per year

  • 0.73kW input ph x 270 hours = 197.1 kWh per year
  • 197.1 kWh x $0.29 per hour = $57.16 for heating

Combined costs for heating and cooling = $110.40

Which AC is cheaper?

The Braemer, the cheaper AC, will cost you about $19.60 more over a year on your electricity bill.

Factoring in the $130 purchase price difference between them, it will take 6.5 years to make this difference back in the form of savings on your energy bill.

Of course, cost is only one factor when buying an air conditioner - there are lots of others involved. You can learn what else to look out for by reading our guides for Split System Air Conditioners and Portable ACs.

Some observations from the marketplace

From our research, we found that most similarly priced models for the same type of AC (e.g. split system, reverse cycle) tend to have a roughly similar efficiency rating to each other.

It was often when models were considerably cheaper (by at least $200) that we saw energy efficiency start to drop noticeably.

Your AC is likely to be more energy efficient if:

  • It’s a recent model, as newer air conditioners are designed with newer technology that is more energy efficient.
  • It’s more expensive up-front to buy.
  • It’s small in size, e.g. 2kW air conditioners, made for very small rooms, will always be more efficient than a large 8kW air conditioner.

Other tips for minimising your air conditioner’s running costs


Make sure you’re using the correctly sized AC for your room

An AC that’s too large for the space will cycle on and off once it reaches the temperature you’ve programmed it to hit, unnecessarily using up extra power.

A unit that’s too small for the space means it won’t quite cool the room as well as you’d like. Certain types of ACs also work better depending on room size.

  • Small rooms: A portable AC is best for a room 20-25m² in size. A room fan may also do the trick.
  • Medium-sized rooms: For rooms 20m²-50m², a window wall unit or a split system works well.
  • Large rooms: A split system AC is the most efficient option for larger spaces 50m² or larger.

Avoid setting the thermostat to extreme temperatures

While it’s tempting to set the air conditioning temperature as low as possible on a 30-degree day, try for 22 degrees instead of 18 degrees.

Aim for 8 degrees lower than the outside temperature. This is thought to be the sweet spot that makes a room comfortable, without the energy drain that comes from setting the thermostat to 18 degrees.

Each extra degree cooler (or warmer) is estimated to add 10% to the running cost of an AC.

Reduce the amount of space to cool

The less space you have to cool, the quicker the room is going to reach that deliciously frosty chill you’ve been craving in summer. You can do this by closing windows and blinds so unwanted sunlight doesn’t warm the room, and closing doors that lead into other rooms; to prevent cool air from leaking out.

Clean or service your air conditioner regularly

Steps to take include testing refrigerant pressure and checking the unit’s airflow and for any leaks. If you’re hiring a professional, do this once annually. You should also clean and replace the filter so it runs efficiently. Filters that are blocked or dirty will obstruct airflow and make an air conditioner less efficient.

Look for eco-friendly features in your air conditioner

These include an eco-friendly mode, inverter technology - which intuitively adjusts the compressor motor speed, a thermostat and timer to give you more control over how much power you’re using, and an auto shut-off mechanism once the AC reaches the target temperature.

Newer AC models are more likely to have a wider variety of eco-friendly features than those than use old technology.